Universal transceivers and supplementary receivers with sparse coding technique option

ABSTRACT

A transmitter is provided having a signal generator configured to generate a sparse code signal where the signal has a substantially small duty cycle of about 0.5% and substantially small pulse widths, with the distance between the pulses defined by the sparse code, and sufficiently low carrier signal level so that the signal can only be detected via a matched receiver.

RELATED APPLICATION

This application is a continuation of U.S. patent Ser. No. 13/269,705,filed on Oct. 10, 2011, the entirety of which is incorporated byreference.

BACKGROUND

1. Field of the Invention

The present arrangement relates to radio frequency transceivers andreceivers. More particularly, the present arrangement relates to codingtechniques for radio frequency transceivers and receivers.

2. Description of Related Art

Garage Door Opener (GDO) and Remote Keyless Entry (RKE) systems and caralarms utilizing RF (radio frequency) signal have been available for afew decades. In the existing technology two coding schemes of fixed codeand rolling code are utilized.

The first generation of such devices utilizes fixed codes which providea relatively low security against hacking by intruders. In a typicalsystem, both the transmitter and the receiver utilize dip switches withtypically 8 to 14 positions. By using standard lab equipment, all thepossible combinations of codes and the common frequencies can beproduced in a matter of seconds and illegal access to a garage or anautomobile or a home can be gained instantaneously.

The second generation of GDO's or RKE systems utilizes rolling codeschemes wherein in every transmission a new code which has amathematical relationship with the previous transmitted codes istransmitted. Devices operating with rolling codes provide comparativelya better protection against unauthorized intrusions than the devicesutilizing fixed codes but they are also prone to unauthorizedintrusions. An individual who has a temporary access to the GDO or RKEremotes, e.g., a parking attendant cannot utilize the copied code from arolling code device to activate a garage door or unlock a car door.However, if the code is captured, the mathematical relationship whichgoverns the code generation eventually can determined and illegal accessto a garage or an automobile can be gained, as there are alreadyaftermarket transmitters sold which utilize rolling codes.

Furthermore, by utilizing simple equipment, hackers can gain illegalaccess to a garage or a car in a matter of hours as opposed to minutesdue to the fact that the rolling codes typically contain longer sequenceof bits.

As explained bellow, both types of systems, i.e., fixed and rollingcodes are vulnerable to security issues and their installation and userequire significant inconveniences.

Vulnerabilities & Disadvantages of Fixed Code Systems

(1) RF Generator and counter can be used for unauthorized intrusion. Anintruder can utilize a simple setup, i.e., an RF (Radio Frequency)signal generator which has pulse amplitude modulation capability inconjunction with a binary counter circuit and an antenna in order toillegally break into a garage or a vehicle. The signal generator isconsecutively tuned to each of the known frequencies at a time whilstthe binary counter circuit produces all the possible binary combinationmodulating the RF signal from the RF generator feeding the antenna.Using such an arrangement for a typical fixed code system utilizing 14bits in a period of less than a minute any garage door can be opened oran automobile lock can be deactivated. I.e., in a 14 bit fixed codescheme, there is a combination of 2¹⁴=4096 possible codes. For a burstlength of 1 mS (millisecond) which typically is required for activatinga GDO, RKE or RFHE a period of 1 mS×4096=4.1 seconds is the requiredtime for each of the commonly used frequencies. In order to go throughthe 10 different common frequencies for producing the 4096 differentcombinations of codes with the binary counter circuit only, it takesonly a time period of about 41 seconds for opening a garage door or anautomobile door.

(2) A Glance at the Dip Switch is sufficient to obtain the code. Anintruder who has a temporary access to a GDO/RKE/RFHE transmitter unit,e.g., a parking attendant, can look at the dip switch combination andcopies the code of the GDO/RKE/RFHE transmitter unit.

(3) Use of universal/Trainable garage Door Opener to copy the code. Anintruder who has a temporary access to a GDO/RKE/RFHE transmitter unit,e.g., a parking attendant, can utilize a universal (Trainable) GarageDoor Opener to copy the code and frequency of the GDO/RKE/RFHE.

(4) Accessibility to the premises even after expiration of thesubscription. In parking lots of apartment building complexes or officebuildings, often the tenants/parking subscribers are changed. However,after tenants leave the complex or their subscriptions to the parkingexpire, they could still use their fixed code/rolling code transmittersand illegitimately access the premises.

(5) Code Grabbing. An intruder who is staying nearby the site canutilize receivers or spectrum analyzers to determine the frequency andthe code.

(6) Universal Garage Door Opener Incompatibilities. Very often auniversal garage door opener cannot learn the frequency or code of anexisting garage door opener. For instance, due to the very shorttransmission time of the code and the super heterodyne receiver in theuniversal garage door openers are not at the appropriate frequencywindow when the transmitter is transmitting. E.g., in the Canadiangarage door openers, only 1-2 seconds of transmission is allowed and theuser has to keep pushing the transmitter button repeatedly so thateventually the universal Garage Door Opener detects the frequency andthe code. Nonetheless, in such cases, special skills are required, i.e.,if the speed of pushing the transmitter button is too fast or too slow,the UGDO does not get trained.

(7) Nuisances and inconveniences with the add-on receivers. Often, whenthe universal garage door opener is incompatible, the user has toutilize an add-on receiver. The addition of such receiver eitherrequires climbing a ladder and wiring or wiring to the door switch whichposes safety risks of falls, electrocution or other accidents/hazardsand expense and delays of hiring a professional for installation whichis nuisance and significant inconvenience to the users. As the variousmodels of door switches operate at different voltages, e.g., 28 V DC,110 AC, 220 AC, the sellers of add-on receivers are hesitant to providetheir units to average users who are lack the sufficient knowledge andexperience and potentially could be subject to risks of falls and/orelectrocution.

Vulnerabilities & Disadvantages of Rolling Code Systems

(1) RF Generator and counter can break rolling codes. Similar to thefixed code case as discussed above, in a rolling code system, anintruder using an RF signal generator and a binary counter circuit wouldstill be able to produce the appropriate code and frequency after sometime and illegally access entry into a garage or unlock a car door.

(2) Rolling codes are subject to hacking. Typically rolling codes arecreated by utilizing a digital feedback control system. Both types LFSR(Linear Feedback Shift Register) and NLFSR (Non-Linear Feedback ShiftRegister) are commonly used in cryptography algorithms such as thosegenerated in rolling code systems. Systems utilizing NLFSR are known tobe more resistant to cryptanalytic hacking than systems utilizing LFSR,i.e., NLFSR systems are breakable after longer periods than LFSRsystems. The aftermarket transmitters which utilize rolling codes havealready become available to the consumers and are currently being soldconfirming that the rolling code systems are not quite as secure as itused to be perceived.

(3) One time access to the garage is sufficient to gain permanentaccess. In a rolling code system, a person who has a temporary access tothe entrance area of the garage, e.g., a worker can easily program thereceiver with his/her rolling code transmitter and illegally access thepremises at later times.

(4) Difficulties associated with adding a new transmitter with RollingCodes. Often the users would need to purchase more GDO transmitters(e.g., as a result of damage, loss or purchase of new vehicles). Newtransmitters are either ordered from the original equipment manufactureror an aftermarket manufacturer or alternatively utilize universaltransmitters capable of handling rolling codes which are available insome automobiles. In order to add any of such transmitters, often inorder to provide the “cryptographic key” to the receiver, the receiverneeds to be trained which necessitates accessing and pressing thetraining button located on the receiver unit while the transmitter istransmitting a signal. The receiver units are commonly mounted adjacentto the garage door opener motors which are installed at 7-10 ft abovethe garage floor. Accessing the receiver is required for every newtransmitter/universal transmitter purchase and requires climbing aladder by some one with sufficient technical background.

(5) Accessibility to the premises even after expiration of thesubscription. Similar to the fixed codes, in parking lots of apartmentbuilding complexes or office buildings, regularly the tenants/parkingsubscribers leave and are replaced with new tenants/parking subscribers.However, after tenants formally leave the complex or their subscriptionto the parking expires, they could still use their fixed code/rollingcode transmitters and illegitimately access the premises.

(6) Code Grabbing. An intruder who stays nearby the site can utilizereceivers to determine the frequency and the code and use the hackedcoding scheme to generate the subsequent codes as there are alreadyaftermarket transmitters sold which utilize rolling codes.

(7) Universal Garage Door Opener Incompatibilities. Often the universalgarage door openers cannot be trained to produce the frequency or therolling codes which necessitates changing the receiver or utilizing anadditional receiver.

(9) Nuisances and inconveniences with the add-on receivers. Often, whenthe universal garage door opener is incompatible, the users utilizeadd-on receiver which necessitates either climbing ladders which posesafety issues such as risks of falls, electrocution or installing wiresto the door switch. Both methods entail expenses and delays of hiring aprofessional for installation which are nuisance and inconvenience tothe users.

Whereby, a superior system which the present invention embodies whichcan provide a higher security with more user-friendly methodology ofactivating and de-activating new transmitters is necessary.

OBJECTS AND SUMMARY OF THE INVENTION

A new class of radio frequency remote control transmitter and receiversystem operating with a novel coding scheme referred to as “SparseCode”is devised. In particular, a new system can be utilized in Garage Door(Gate) Openers (GDO), Universal Garage Door (Gate) Openers (UGDO),Remote Keyless Entry (RKE) systems or Radio Frequency Home Entry (RFHE)systems.

The new system can operate as either a standalone UGDO or asupplementary receiver for situations which existing UGDO's areincompatible with the receivers. Also, a transmitter built according tothe new system in conjunction with a receiver, referred to as“supplementary receiver” accommodates the users who need to add moregarage door opener transmitters but copies of the existing transmitterscannot be obtained or are not easily available. A supplementary receiverbuilt according to the present invention can be utilized in conjunctionwith a transmitter which uses the regular (SparseCode/fixed code/rollingcode).

According to a preferred embodiment of the present invention, theuniversal/supplementary receiver is installed over wall switch of agarage door opener by a snapping clamp mechanism and contains amechanical actuator. When the receiver receives an activation signalfrom the pertinent transmitter, the built-in actuator exerts a momentaryforce on the button of the wall switch and subsequently the garage dooris activated. This embodiment eliminates the need for any drilling,wiring or climbing a ladder which is typically necessary whenprogramming a rolling code receiver or adding a supplementary receiverwhich brings about considerable inconveniences and often require use ofexperts.

The new coding system, i.e., “SparseCode”, provides a superior securityover the existing systems utilizing fixed/rolling code schemes. Thefrequency and code of a signal from a transmitter which transmitssignals utilizing SparseCode cannot be captured by devices known as“code grabbers”, Universal Garage Door Openers (UGDO) or spectrumanalyzers (SA).

Devices such as Remote Keyless Entry (RKE) Transmitters, regular (singlefrequency) Garage Door Openers (GDO), universal Garage Door Openers(UGDO) or Radio Frequency Home Entry (RFHE) Systems with “SparseCodecapability” can easily be programmed to transmit the appropriateactivation codes for activating any receiver with “SparseCode”capability. The programming is simply done by key entries using onlythree or four keys available on the transmitters. Any transmitter withSparseCode capability can be programmed utilizable for activation ofmultiple devices even with different applications, e.g., GDO, RKE andRFHE receivers or even home appliances, medical, industrialapplications, etc.

Programming of a transmitter with SparseCode capability is done byentering the pertinent Identification Code (ID-CODE). After completionof programming, each ID-CODE is assigned to a key on any transmitter.

According to the present invention, there are two types of receiverswith SparseCode capability, pre-programmed and programmable. In thepre-programmed system, the programming is performed at the factory,whereas, the programmable receiver is programmed by the user and it canhandle various codes for various subscribers. Using a remote control oralternatively the receiver keys, the receiver is programmed by firstentering a Programming Access Code (PAC) and subsequently entering thepertinent “ID-CODE”. PAC provides the validation for accessing to thereceiver which is used for both programming a new ID-CODE for deletingID-CODE's of expired subscriptions.

Any transmitters with SparseCode capability, e.g., OEM transmitters,universal transmitters can be enabled by programming the ID-CODE tooperate in conjunction with the universal/supplementary receiver withSparseCode capability.

The receivers with SparseCode capability utilize a new method fordetection of low duty cycle data which eliminates the need forsynchronizer circuits or data scrambling schemes.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 depicts a block diagram for a universal/supplementary receiverwhich utilizes a mechanical actuation mechanism to actuate a wall switchto actuate a garage door opener, wherein the receiver is either a fixedcode or sparse code type;

FIG. 2 depicts a possible mechanical implementation of the block diagramdepicted in FIG. 1;

FIG. 3 depicts a block diagram for an universal/supplementary receiverwhich utilizes a mechanical actuation mechanism to actuate a wall switchto actuate a garage door opener, wherein the receiver is a rolling codetype and contains an extra switch for the learn function in the rollingcode receiver;

FIG. 4 depicts a possible mechanical realization of the block diagramdepicted in FIG. 3 wherein the rolling code learn button is located onthe bottom of the housing for the receiver;

FIG. 5 depicts a possible implementation for connecting theuniversal/supplementary receiver to a wall switch in which use of screwsfor installation is not required wherein bracing jaws are utilized forsnapping on the wall switch;

FIG. 6 is a depiction of a dissected possible mechanical realization ofthe block diagram depicted in FIGS. 1 and 4 wherein by utilizing a camshaft and shape memory alloy wires to implement a low profileuniversal/supplementary receiver;

FIG. 7 depicts an alternative possible mechanical realization of theblock diagram depicted in FIGS. 1 and 4 wherein the receiver isinstalled adjacent to a wall switch;

FIG. 8 depicts a universal transmitter with SparseCode capabilityimplemented in an overhead consol;

FIG. 9 depicts a universal transmitter with SparseCode capabilityimplemented in a visor;

FIG. 10 depicts a universal transmitter with SparseCode capabilityimplemented in a rear view mirror;

FIG. 11 depicts a universal transmitter with SparseCode capabilityimplemented in a fob;

FIG. 11 depicts a universal transmitter with SparseCode capabilityimplemented in a key fob;

FIG. 12 is a depiction of the format of a word generated by atransmitter utilizing SparseCode;

FIG. 13 depicts a possible block diagram for a SparseCode transmitter;

FIG. 14 depicts a flow chart for training procedure of a transmitterwith SparseCode capability;

FIG. 15 depicts the block diagram of a receiver with power saving whichcan be utilized for the present invention to save power and possibly usea battery;

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As described above, existing technologies, i.e., both rolling and fixedcode systems suffer from security issues and significant inconveniencesduring the initial set up. The present invention resolves these issues.By utilizing a new coding system referred to as SparseCode the problemsassociated with rolling and fixed code systems are avoided. As describedbelow, SparseCode is too fast and too short to be “grabbed” or “learned”by a UGDO or even by use of sophisticated lab instrument such as aspectrum analyzer. Furthermore, use of SparseCode provides anastronomical number of combinations of codes which practically is notreproduce-able by using a counter circuit and in conjunction with asignal generator.

As a major advantage of SparseCode systems, a transmitter withSparseCode capability can be trained to activate any receiver withSparseCode capability. The training is performed by entering anidentification code (ID-CODE) using the keys on the transmitter.According to this embodiment of the present invention, the only methodfor training the GDO/RKE/RFHE transmitters is by key entries enteringID-CODE. The ID-CODE includes both code and frequency information(bandwidth and center frequency). Hence, according to the presentinvention there is no need to have a physical access to the receiver foradding the base code, “cryptographic key”, which is the method used inrolling codes and necessitates climbing a ladder.

Often, there are compatibility issues when using UGDO's, e.g., theycannot detect the frequency or the code of the reference transmitter orcannot produce the proper rolling code. In such situations, when theoriginal or a supplementary receiver SparseCode capability is utilized,addition of a new transmitter simply involves entering the pertinentID-CODE in the transmitter.

According to another preferred embodiment of the present invention, areceiver with SparseCode capability can handle multiple ID-CODE's and isremotely accessible for programming in a new ID-CODE or deleting an oldID-CODE. This is done by first entering a Programming Access Code (PAC)which is used to allow access by the authorized person(s) to thereceiver codes.

As described in below, amongst the major security advantages of systemsutilizing SparseCode is the safety to hacking and illegal copying whilstthe legal copying is quite simple and is done in a matter of minuteswith simple key entries.

For a receiver built according to the present invention utilizingSparseCode even with the use of an RF signal generator in conjunctionwith a binary counter circuit and an antenna, it would take astronomicalnumber of years to break into a garage, home or an automobile. This ismathematically demonstrated bellow that by utilizing SparseCode systemprovides an astronomical number of combinations of codes andconsequently is virtually unbreakable.

In typical data communication systems at certain instances the dutycycle can become too low or too high. In order to avoid loss ofsynchronization different schemes such as data scrambling or bipolarsignal are utilized but such schemes would not be appropriate in ofSparseCode, as SparseCode require a low duty cycle. In the SparseCodesystems however, for obtaining synchronization preambles with very lowduty cycles are utilized.

According to an embodiment of the present invention a supplementaryreceiver is installed adjacent to or atop of garage door opener wallswitch, and is interfaced with the switch instead of the existing garagedoor opener receiver output. Since these switches are generallyinstalled at accessible heights, installation of supplementary receiverswould not require ladder climbing. Interfacing of a supplementaryreceiver with the switch can be done by simply either connecting wiresfrom supplementary receiver to the switch, or installing thesupplementary receiver atop of the switch by either screwing thereceiver to the wall or by utilizing the snapping mechanism which isbuilt-in the supplementary receiver to attach to the wall switch or byutilizing another type of supplementary receiver which is installed onthe wall adjacent to the garage door opener wall switch.

According to a preferred embodiment of the present invention the needfor wiring is eliminated by using a snap-on overlay mechanism whichmechanically activates the wall switch when needed.

Different methods can be utilized for mechanical activation of the wallswitch, e.g., use of a shape memory alloy (SMA) wire/strip, an electricmotor, a solenoid, a bimetal strip. However the preferred embodimentaccording to the present invention for producing mechanical movements isuse of shape memory alloys in which by passing a current the generatedheat would change the shape of the alloy resulting in the appropriateforce to push the garage door switch. There are numerous types of shapememory alloys, e.g.: Ag—Cd, Au—Cd, Cu—Al—Ni, Cu—Sn, Cu—Zn, Cu—Zn—X(X=Si, Al, Sn), Fe—Pt, Mn—Cu, Fe—Mn—Si, Co—Ni—Al, Co—Ni—Ga, Ni—Fe—Ga,Ti—Pd, Ni—Ti, Ni—Mn—Ga.

One of the most commonly used shape memory alloys (SMA) is TiNi, i.e.,Titanium-Nickel alloy also referred to as Nitinol. Shape memory alloyshave pseudo-elastic properties of the metal during the high temperature(austenitic) phase. They can undergo large deformations in their hightemperature state and then instantly revert back to their original shapewhen the stress is removed. As an electrical current is passed throughan SMA wire or an SMA strip heat is generated, the austenitic state ofchanges to martensitic state causing the desired effect, e.g.,shrinkage, bending etc. This criterion is utilized in the presentinvention as a preferred choice for the implementation of an actuator.In an overlay enclosure added on top of a garage door opener switch aSMA strip/wire is used to create movement to press a garage door openerswitch.

FIG. 1 depicts a possible implementation of a block diagram foruniversal/supplementary receiver 100 according to the present invention.Antenna 106 couples the radio frequency signal to a fixed code receiveror SparseCode receiver 108. Upon reception of activation signal,receiver 108 in turn produces a signal activating timing circuit 110which produces a high current/voltage state for a short period of time,e.g., 1 second to activate a electromechanical actuator 112 which inturn produces movements of a lever in order to exert force on the button103 of wall switch 102. Electromechanical actuator can be composed of anelectromagnet, or an electric motor producing a linear movement or arotary motor such as a step motor or a system utilizing SMA wires/stripsor bimetal strips or any other type of electromechanical actuation.Since wall switch 102 is covered by the universal/supplementary receiver100 housing, universal/supplementary receiver 100 is equipped withexternal switch 114 which functions as a substitute for wall switch.Upon a momentary push of external switch 114, a high current/voltagestate for a short period of time, e.g., 1 second is generated in orderto activate electromechanical actuator 112 which in turn producesmovements of a lever to exert force on the button 103 of wall switch102.

FIG. 2 depicts a physical implementation for the block diagram ofFIG. 1. An overlay enclosure 120 is utilized which includes an openingto accommodate protrusion of standard wall switches commonly availablein the market into the enclosure 120. According to FIG. 2, wall switch102 is secured to the wall via two screws 168 and 170. The overlayenclosure 120 is secured to the wall by utilizing screws 124 and 128utilizing built-in screw slots 122 and 126 in hosing. As a preferredchoice for antenna, a spiral antenna 106 is utilized in the depiction ofFIG. 2 which couples the RF signal to receiver 108 which provides anoutput to timing circuit 110. A pair of wires connects the output of thetiming circuit 110 to electromechanical actuator 112. Upon receiving anactivation signal, a high current/voltage state is generated for a shortperiod of time, e.g., 1 second to activate an electromechanical actuator112 which in turn produces movements of a lever and exerts force on thebutton 103 of wall switch 102. Universal/supplementary receiver 100 ispowered via an external AC to DC power supply which is plugged into anoutlet. The external power supply is connected touniversal/supplementary receiver 100 via a connector 113 on the sidewall of enclosure 120.

FIG. 3 depicts a possible implementation of a block diagram foruniversal/supplementary receiver 100. Antenna 106 couples the radiofrequency signal to a rolling code receiver 109. Upon reception ofactivation signal, receiver 109 in turn produces a signal activatingtiming circuit 110 which produces a high current/voltage state for ashort period of time, e.g., 1 second to activate electromechanicalactuator 112 which in turn produces movements of a lever in order toexert force on the button 103 of wall switch 102. Since wall switch 102is covered by the universal/supplementary receiver 100 housing, the wallswitch is not accessible. Hence universal/supplementary receiver 100 isequipped with external switch 114 which functions as a substitute forwall switch. Upon a momentary push of external switch 114, a highcurrent/voltage state for a short period of time, e.g., 1 second toactivate an electromechanical actuator 112 which in turn producesmovements of a lever in order to exert force on the button 103 of wallswitch 102. External switch 116 is connected to rolling code receiver109 and is utilized as the means for alerting the receiver 109 for thelearn function which is typically used in rolling code receivers duringtraining procedures.

FIG. 4 depicts a possible physical implementation for the block diagramof FIG. 3. Overlay enclosure 120 includes an opening to accommodateprotrusion of standard wall switches commonly available in the marketinto the enclosure 120. According to FIG. 4, wall switch 102 is securedto the wall by means of screws 168 and 170. Overlay enclosure 120 isindependent of wall switch 102 is secured to the wall by means of screws124 and 128 wherein screw slots 122 and 126 are utilized in housing 120in order to contain screws. As a possible choice for antenna, spiralantenna 106 is utilized and couples the RF signal to rolling codereceiver 109 and timing circuit 110 respectively. A pair of wiresconnects the output of timing circuit 110 to electromechanical actuator112. Upon receiving an activation signal, timing circuit 110 generates ahigh current/voltage state for a short period of time, e.g., 1 secondwhich in turn activates electromechanical actuator 112 whichsubsequently produces movements of a lever in order to exert force onthe button 103 of wall switch 102 which in turn activates the garagedoor. Universal/supplementary receiver 100 is powered via an external ACto DC power supply which is plugged into an electrical outlet. Theexternal power supply is connected to universal/supplementary receiver100 via a connector 113 on the side wall of enclosure 120. Externalswitch 116 located on the bottom portion of housing 120 is connected toand engaged with rolling code receiver 109. External switch 116 isutilized as the means for activating the learn function of receiver 109such activation is typically necessary when a rolling code receiverlearns the base code (cryptographic key) of a rolling code transmitter,“cryptographic key”, during the training procedures.

FIG. 5 depicts the front and side view sections for a possibleimplementations of clamping system used for attaching auniversal/supplementary receiver to garage door opener wall switch 102.According to this preferred embodiment of the present invention, thereis no need to drill any holes for installing the universal/supplementaryreceiver. Housing 130 includes a rectangular opening 105 which isslightly larger than the rectangle in the back of standard garage dooropener wall switches used in the industry. For non standard switches,user can replace it with a common wall switch type or add a parallelstandard. Alternatively the user can utilize the type of receiver whichis mounted adjacent to the wall switch depicted in FIG. 7 which isdescribed below. In the course of installation opening 105 inuniversal/supplementary receiver unit is placed around the garage dooropener wall switch 102 and the housing is pushed against the wall. Bypushing a lever with a linear or a rotational mechanism, a clampingmechanism snaps onto the wall switch by scoring superficial cut into theswitch. According to the implementation depicted in FIG. 5, two pairs ofblades are used to score and penetrate into the four corners of wallswitch 102. Blade pairs 136, 137 are attached diagonally to the top jaw132. Similarly, blade pairs 140, 141 are attached diagonally to the topbottom jaws 138. The movements of jaws 136 and 138 are regulated byrailing and spring loaded mechanisms so that whenuniversal/supplementary receiver is snapped on the wall switch 102, thebottom jaws 138 provides the adequate force utilizing spring loading.Pair of rods 144, 145 functions as guide rails and partially areprotruded into the lateral portions of jaw 132. The other ends of therods 144 are secured into pair of support flanges 148. A pair of springs142, 143 partially encompasses rods 142, 143 and is extended fromflanges 142, 143 into top jaw 132. Similarly, pair of rods 152, 153functions as guide rails which are partially protruded into the bottomof lateral portions of jaw 138. The other ends of the rods are securedinto housing 130. A pair of springs 134, 135 encompasses rods 152, 153and extends from housing 130 from the bottom into mid jaw 138. Springpairs 134, 135 are partially extended into holes 150, 151 locatedlaterally in jaw 138. As a result, the bottom jaw is spring loaded tohousing 130. In an alternative configuration bottom jaw 138 can beaffixed to housing 130 and only top jaw 132 can be spring loaded.

Installation of the described universal/supplementary receiver via useof the clamping mechanism can be done by an individual without expertiseor special skills, i.e., opening 105 of the housing 130 ofuniversal/supplementary receiver 100 is placed around wall switch 102and moved towards the wall until firmly touches the wall. Subsequentlyuser moves/turns the snapping mechanism. According to implementation ofFIG. 5, the snapping mechanism utilizes a rotational method utilizing arotational element 160 which is secured to the housing via a bolt 162.Rotational axle 164, is turned by rotational element 160 connected to anoff-axis rod 158 which protrudes into an off axis hole in cam 154. Cam154 is installed to the housing 130 via axle 156. As a result of turningof rotational element 164, cam 154 is turned around its axis which inturn pushes jaws 132 downward and subsequently blade pairs 136 and 140score into the four corners of the wall switch 102. In FIG. 5, elementlabeled 160 represents either a lock cylinder or other means ofproviding a rotational movement. When a lock mechanism is utilized a keyis inserted into lock cylinder 160 and subsequently the key is turned toa lock position.

Depiction of FIG. 5 represents a possible scheme for attaching auniversal/supplementary receiver to a Garage Door Opener wall switchwherein 4 blades score into the wall switch. However, other schemesusing similar concept are possible and are within the scope of thepresent invention, i.e., either by using blades, or using other types ofsharp edges or sharp points or other means for clamping on the wallswitch are possible.

Another approach is electrical activation of the clamping mechanism. Onepossible approach an electric motor/electromechanical actuator coupledto the locking mechanism. Alternatively scoring into the wall switch bymeans of utilizing heated wires (such as SMA wires) can be utilized asthe means for attaching of the housing of the receiver to the wallswitch. A possible implementation could be by passing an electricalcurrent through an SMA (e.g., Nitinol) wire, as the temperature of thewire increases to near or above the melting point of the plastic usedfor the wall switch at the same time as the SMA wire shrinks in lengthas a result of heat, the SMA wire superficially enters into the wallswitch. Metal sheets can subsequently enter in the scored space asfurther support. Electrical activation of the clamping mechanism can beaccomplished by means of pressing a button or turning a key in a lockwhich is connected to an electrical switch.

Alternatively, non-sharp objects such as surfaces with high frictionindex, e.g., rubbers, rough surface such as sandpapers or alike,glues/epoxies, Velcro, suction cups or heated surfaces can be utilizedas a part of a clamping process. Other possible approaches are screwingor gluing the universal/supplementary receiver to the wall switch or thewall.

FIG. 6 depicts a dissected (bottom jaw is not shown) image of a lowprofile electromechanical actuator implementation of the presentinvention using a shape memory alloy (SMA). Garage door opener wallswitch 102 is pre-installed on a wall using screws 168 and 170 and iswired to a garage door opener mechanism. The electromechanical actuatormechanism is composed of cam shaft 180 secured in bushings 184 and 186each attached to a side wall of the housing for universal/supplementaryreceiver. Cam shaft 180 includes a shaft and other components, i.e., cam182, tab 188 and tab 202. Torsion spring 200 is secured on one of thefar ends of cam shaft 180 and is inserted in a hole 204 located inbushing 184 and is wound against tab 202. A mild spring loading functionis obtained by use of torsion spring 202, as a result normally cam 182is kept away from wall switch 102 and cam shaft 180 is pressedcounterclockwise. Tab 188 is located at the other side of cam shaft 180close to busing 186. Tab 188 contains a groove to contain part of SMAwire 190. SMA wire 190 is guided via a guiding mechanism 192 so that SMAwire 190 extends upward and as a result extra lengths of SMA wire lengthis utilized and consequently sufficient wire displacement is obtainedduring the activation. The two ends of SMA wire 190, labeled 196 and198, are secured in holes located in flange 194 attached to the housingof universal/supplementary receiver. SMA wire ends 196 and 198 areconnected to the pertinent timing circuit (not shown). Upon activationof universal/supplementary receiver, the pertinent timing circuitproduces an electrical current pulse which passes through SMA wire 190,which produces heat in SMA wire 190 resulting in shrinkage of SMA wire190 and in turn tab 186 moves towards the wall and cam 182 pressesbutton 103 of the garage door opener wall switch 102 garage door openermechanism activates.

FIG. 7 depicts a possible method for an alternative type of auniversal/supplementary receiver constructed according to the presentinvention wherein the receiver is installed adjacent to a wall switch.This embodiment represents another possible mechanical implementation ofthe block diagram depicted in FIGS. 1 and 3 wherein the receiver isinstalled adjacent to a wall switch.

In this embodiment a lever extending out from an electromechanicalactuator located in a receiver housing is used to activate the wallswitch. The receiver housing is installed at a certain distance from awall switch such that the extension of the arm can interact with thebutton on the wall switch.

As depicted in FIG. 7, wall switch 102 is secured to the wall by meansof screws 168 and 170 and enclosure 210 is independently secured to thewall by means of screws 124 and 128. Screw slots 122 and 126 areutilized in housing 210 for containing screws 124 and 128. Enclosure 210includes an opening 212 to accommodate lever 214 extending outside ofenclosure 210. Tip of lever 214 has a screw hole which accommodatesthreaded piston 218. Cylindrical pad 216 which preferably is made ofsoft material such as rubber or plastic is connected to threaded piston218. Knob 220 is attached at the other end of threaded piston 218. Thechoice of where enclosure 210 is installed on the wall is made based onaligning cylindrical pad 216 above button 103 of the garage door openerwall switch 102. By turning knob 220 the cylindrical pad 216 is broughtclose to button 103 of the garage door opener wall switch 102. Uponactivation of receiver enclosed in housing 120, the built-inelectromechanical mechanism provides the proper movement of lever 214which in turn cylindrical pad 216 presses button 103 of the garage dooropener wall switch 102. Universal/supplementary receiver depicted inFIG. 7 is equipped with external switch 114 which functions as asubstitute for wall switch. Upon a momentary push of external switch 114the built-in electromechanical mechanism provides the proper movement oflever 214 which in turn cylindrical pad 216 presses button 103 of thegarage door opener wall switch 102.

Another embodiment of the present invention is a transmitter capablegenerating a novel coding scheme of data transmission referred to as“SparseCode” and a receiver capable of deciphering SparseCode. Theadvantage use of SparseCode is its security and ease programming anytransmitter with SparseCode capability. Different devices can be builtto function as universal transmitter (UT), with SparseCode capability,e.g., universal garage door openers (UGDO), remote keyless entry (RKE),and radio frequency home entry systems (RFHE).

There are gate or garage door opener switchers which incorporate two orthree buttons for different operations, i.e., open, close and stop. Insuch a situation two or three universal receivers such as receiver ofFIG. 7 can be utilized. Alternatively, a receiver incorporating doubletriple actuator similar to depictions of FIGS. 2, 4, 5, 6 and 7 can beutilized.

FIG. 8 depicts a universal transmitter/with SparseCode capabilityimplemented in an overhead console wherein only three buttons areavailable to the user. Such a universal transmitter can be utilized agarage door opener and/or radio frequency home entry systems and/orappliance controls. An LED is available for the normal operation of theuniversal transmitter as well as aiding the user during programming theSparseCode.

FIG. 9 depicts a universal transmitter with SparseCode capabilityimplemented in a visor wherein 4 keys are available to the user. An LEDis available for the normal operation of the universal transmitter aswell as aiding the user during programming the SparseCode.

FIG. 10 depicts a universal transmitter with SparseCode capabilityimplemented in a rear view mirror wherein 6 keys are available to theuser. An LED is available for the normal operation of the universaltransmitter as well as aiding the user during programming theSparseCode.

FIG. 11 depicts a universal transmitter with SparseCode capabilityimplemented in a fob wherein 6 keys are available to the user. An LED isavailable for the normal operation of the universal transmitter as wellas aiding the user during programming the SparseCode.

FIG. 12 depicts a universal transmitter with SparseCode capabilityimplemented in a key fob. One side of the key fob contains the commonkeys typically used for remote keyless entry functions. On the secondside 6 keys and an LED are available to the user for SparseCodecapability.

Means of Generating and Detecting SparseCode

As discussed above, user of rolling codes and fixed codes for garagedoor openers and remote keyless entry systems are faced withdifficulties in their initial setup, training universal transmitters,adding new transmitters and various security issues. The systemconstructed according to the present invention, however, utilizesspecial hardware to generate a signal (referred to as “SparseCode”)which cannot be hacked or copied as it utilizes an exceedingly low dutycycle and short pulse widths. As a result the carrier cannot be detectedand effectively makes the system invulnerable from the signal gettingcopied by unmatched any receiver. A user of the devices constructedaccording to the present invention has the ability to enter thepertinent code by key entries on of the transmitter (rather thanpressing the learn key of the receiver in the rolling code system whichnecessitates climbing a ladder). The presence thermal (Johnson) noise inreceivers (Noise Power=kTB, where k is the Boltzmann's constant, T isthe temperature in Kelvin and B is the receiver Bandwidth) isunavoidable and necessitates matched bandwidth to pulse width of data,however, slight increase or decrease in bandwidth or center frequencyproduces excessive ISI (Inter-Symbol Interference). Thereby for thepresent invention only a matched receiver can detect the presence ofsignal transmitted. On the other hand, if an unmatched receiver withexcessive bandwidth, including a spectrum analyzer (which is effectivelya receiver with a sweeping local oscillator with a constant unmatchedbandwidth) is used, the received signal would be buried in thermalnoise. Only a matched receiver, i.e., a receiver with a posterioriintelligence of bandwidth, pulse width, frequency and coding scheme.

SparseCode generated by a transmitter according to the present inventionhas a typically some but not necessarily all of characteristics asfollows:

(1) Small duty cycle (typically <0.5%), a duty cycle of higher than 0.5%could be utilized. however, it would be more vulnerable to hacking.

(2) Short pulse widths ranging from a few to several microseconds.

(3) The data is subdivided into several groups, e.g., 4 groups.

(4) Each data group is preceded with a unique preamble.

(5) The data and preambles are designed so that two or more consecutivehighs are avoided.

(6) Frequencies of for different devices are not unique.

(7) Pulse widths and consequently receiver bandwidths for differentdevices are different.

(8) The carrier signal level is selected so that the signal to noiseratio at the receiver is sufficiently low not detectable with anunmatched receiver. According to a preferred embodiment, the carrierfrequencies of each burst are different.

Utilization of the described characteristics when the transmitteroperates at low power results in a low signal to noise ratio at thereceiver which requires a matched receiver as the signal characteristicscannot be detected with any sweeping Superheterodyne circuitry due toboth time and frequency ambiguities, and incidental FM. I.e., the RFenergy is only present for an extremely short period of time incomparison to the sweep scan time of the universal (trainable) garagedoor openers or spectrum analyzers, and the resolution bandwidth of theuniversal (trainable) garage door openers or spectrum analyzerspractically would not match with the data which in turn results in ISIand signal spread in both frequency and time which generates excessiveambiguity for an unmatched detection mechanism. Even if the sweep timeof a super-heterodyne trainable garage door opener was to be shortened,the signals transmitted from a transmitter built according to thepresent invention would not be detectable due to incidental FM. When thesweep time is reduced, the sweep speed increases and consequently thesweep signal would include abundance of “incidental FM” signals oreffectively an FM signal with high index of modulation composed ofnumerous sidebands wherein the main carrier is no longer clearlyidentifiable. The numerous sidebands would interfere with the signaldetection process and impede the frequency identification in thespectrum analyzers or super-heterodyne universal garage door openers.

As discussed above SparseCode includes a preamble and data which servesas the means for signaling the receiver to synchronize with the upcomingdata. As a result, repeated bit stream for data synchronization is notnecessary and the receiver would respond to the first transmission.Generation of certain data which could be confused as preamble isavoided in order to avoid erroneous synchronizations. This could beaccomplished in different fashions. One possible way is to make thepreamble bits with certain spacing different than those of data bits.Another method is by avoiding the codes which would result in datastream identical to the preamble.

According the present invention making a legitimate copy of aGDO/RKE/RFHE transmitter can be done by the owner or an authorizedperson who is given the pertinent “training code”, ID-CODE, e.g., a25-digit number composed of the four digits 1, 2, 3 and 4. In the threebutton style transmitters, however, two key can be pressedsimultaneously to represent the fourth key, e.g., when the keys 1 and 3are pressed simultaneously correspond to the 4 key.

The training of the transmitter is performed by entering “ID-CODE” viathe keys on the GDO/RKE/RFHE transmitters. The “ID-CODE” contains bothfrequency and code information. In a preferred embodiment according tothe present invention, the combination of single key and double keyentries are utilized which increase the possible number of symbols. Adouble key entry is composed of simultaneously pressing two keys. Forinstance according to this embodiment of the present invention, in a 4key system when simultaneously pressing the keys “4” and “1” theresultant action would correspond to “5”, similarly when simultaneouslypressing the keys “4” and “2” the resultant action would correspond to“6”, or simultaneously pressing the keys “4” and “3” the resultantaction would correspond to “7”.

A variety of devices/systems (e.g., a regular garage doortransmitter/receiver, a universal transmitter or a trainable/universalgarage door opener transmitter/receiver, a key fob or house key with afob transmitter with a receiver) with SparseCode capability benefitsfrom its features, i.e., new codes for different applications can beprogrammed, signals emitted from a transmitter are very secure as theycannot be copied by a super-heterodyne trainable garage door opener,spectrum analyzers. Hence, when a key fob with SparseCode is temporarilyleft by a non-owner (e.g., parking attendant, auto repair shop), theSparseCode cannot be illegitimately copied even when utilizing anordinary UGDO.

A transmitter built according to the present invention utilizesSparseCode which is a sparse binary code, i.e., a long binary stringwith an extremely small duty cycle provides an astronomical number ofpossible combinations.

As a numerical example for demonstrating the merits of the SparseCodesystems, a transmission time of 0.1 S and a bit rate of 400,000 bps areselected. Every stream of transmission includes (K=0.1 S×400,000 b/s)40,000 bit slots. If a duty cycle in the range of 0.2-0.4% is selected,then for each transmission there would be between L=800 to M=1,600 bitstransmitted. The possible number of combinations, N, is:

$N = {\begin{pmatrix}K \\L\end{pmatrix} + \ldots + \begin{pmatrix}K \\{L - i}\end{pmatrix} + \ldots + \begin{pmatrix}K \\M\end{pmatrix}}$

Utilizing the Stirling's approximation,

${n!} \approx {\sqrt{2\; \pi \; m}\left( \frac{n}{e} \right)^{n}}$

and using the SparseCode assumption, i.e., K>>L and K>>M, yield that thenumber of combinations N is:

$N > {\sqrt{\frac{2\; K}{\pi \left( {M + L} \right)}}\left( {M - L + 1} \right)\left( \frac{2\; K}{M + L} \right)^{\frac{M + L}{2}}}$

For K=40,000, L=800 and M=1,600 the number of combinations:

N>2.61×10¹⁸³⁰

Using a setup described above to produce all the combinations(2.61×10¹⁸³⁰) in order to make an illegal entry, the require time periodcalculates to be:

$\frac{2.61 \times 10^{1830}}{\begin{matrix}{\left( {400,000\mspace{14mu} {Bits}\text{/}s} \right) \cdot \left( {3600\mspace{14mu} s\text{/}{hrs}} \right) \cdot} \\{\left( {24\mspace{14mu} {hrs}\text{/}{day}} \right) \cdot \left( {365\mspace{14mu} {day}\text{/}{year}} \right)}\end{matrix}} = {2.08 \times 10^{1817}}$

years.

This demonstrates that a typical realization of SparseCode with even thelimited number combinations which only includes the very short dutycycle patterns (limited in the range of 0.2-0.4%) an astronomicalcombination of codes are created.

The following is a possible implementation example which demonstratesfunctionality of a SparseCode-based system:

Bit rate=400,000 bpsPulse width= 1/400,000 bps=2.5 μSNumber keys available on the transmitter for programming=Number Base: 4Number of base-4 digits used for ID-CODE=25Number of groups in ID-CODE=5

Example for Key Entry for ID-CODE=43312, 22312, 21132, 33443, 24344

Conversion from Key Entry digits (1, 2, 3, 4) to base-4 digits (0, 1, 2,3):43312, 22312, 21132, 33443, 24344−11111, 11111, 11111, 11111, 11111=32201, 11201, 10021, 22332, 13233₍₄₎Subdividing 25 base-4 digits into 5 groups:(32201)₍₄₎=3×4⁴+2×4³+2×4²+0×4¹+1×4⁰=(897)₍₁₀₎(11201)₍₄₎=1×4⁴+1×4³+2×4²+0×4¹+1×4⁰=(353)₍₁₀₎(10021)₍₄₎=1×4⁴+0×4³+0×4²+2×4¹+1×4⁰=(265)₍₁₀₎(22332)₍₄₎=2×4⁴+2×4³+3×4²+3×4¹+2×4⁰=(702)₍₁₀₎(13233)₍₄₎=1×4⁴+3×4³+2×4²+3×4¹+3×4⁰=(495)₍₁₀₎

FIG. 13 depicts a portion of word generated by a transmitter utilizingSparseCode for the discussed example depicts a portion of word generatedby a transmitter utilizing SparseCode for the discussed example (onlygroups 1 and 2 group of the ID-CODE are shown). Each group is composedof a preamble string followed by a data string. The strings generated inthe 1st and 2nd groups are produced as a result of the 1st 10 keyentries, i.e., 43312 and 22312 which correspond to 32201 and 11201 inbase 4 which respectively correspond to 897 and 353 in base 10. Each ofthese numbers is represented in the data strings with only one high bit.The location of high bit in the data string is bit number 897 in thefirst data string and 353 in the second data string. I.e., the locationof the only high bit in every data string is determined by the countingfrom the start (bit 1 after preamble) until the number corresponding tothe pertinent portion of ID-CODE. This is shown in the FIG. 8 depicts aportion of word generated by a transmitter utilizing SparseCode for thediscussed example, wherein the data string of group 1 bit number 897 isset to 1 and the remaining bits are all 0's. Similarly, in the dataportion corresponding to group 2 only bit number 353 is set to 1 and theremaining bits are all 0's. Each of the data transmissions are precededby a known preamble typically composed of 1000 bits. Preambles includeguard regions (e.g., 50 bits on each side), i.e., a long string of 0's.The all zero guard regions are utilized in order to avoid possibleoccurrence of a 1 from the preamble close to a 1 from the data string.

Furthermore, in order to keep the duty cycle appropriately low (lessthan 0.5%), preambles include a maximum of 4 high bits in the remaining900 bits.

A receiver with SparseCode capability has a posteriori knowledge of thepertinent preambles.

Training Procedure for Universal Transmitters and SupplementaryReceivers

According the present invention making a legitimate copy of a GDO/RKEtransmitter can be done by the owner or an authorized person who isgiven the pertinent identification code, ID-CODE. The ID-CODE is enteredvia the keypad keys. In a preferred embodiment simultaneous key entriesare utilized, i.e., if only four keys are utilized, addition of pressingtwo keys simultaneously provides 6 addition choices. According to thepresent invention the only method for another transmitter to be trained(learning the frequency and the code) from a transmitter utilizingSparseCode is by manually entering ID-CODE via the keypad. Variety ofdevices for different applications can be manufactured to haveSparseCode capability, e.g., a regular transmitter, a universaltransmitter or a trainable (universal) garage door opener. This is oneof the main improvements in the security of a transmitter withSparseCode, i.e. copying of such a code and the frequency by means of asuper-heterodyne trainable garage door opener, spectrum analyzers whichperforms frequency sweeps is not possible.

According to the present invention, the manufacturer supplies to theuser an identification code (ID-CODE) which includes both the code andfrequency information. This information is entered into the universalremote for instance via only 3 or 4 keys which is the method for makingadditional copies of a GDO/RKE transmitter.

For instance, if there are 1024 frequencies in the band of interest, thefrequency can be entered via only 5 key entries as (250)₁₀=(3322)₄. Fora bit rate of 10 kbps, and a transmission time of 0.01 second, the totalnumber of bit slots is K=1000. A selection of a SparseCode with a lengthof 5-8 bits, i.e., L=5 and K=8 would require over 50,000 years toproduce all the combinations. To assign bits sparsely with a sufficientseparation which would not be identifiable by a super-heterodynetrainable transmitter, the bit slots (K=1000) can be divided into 8sections of 125 bits wherein in each section there is maximum of one bitpossibly present. The location of each bit within the pertinent sectionis described with four digits which are entered via the 4 keys presenton the transmitter. To cover the entire K=1000 bit slots, 4×4=16 entriesare necessary.

In a possible scenario, the user first alerts the Trainable Transmitter(TT) by pressing two keys simultaneously (e.g., 1 and 2 keys). After acertain period of time (e.g., 8 seconds) the TT responds by an LEDblinks to inform the user that the training mode is initiated. Then theuser presses the key which the user intends to utilize after thesubsequent training procedure. The LED blinks multiple times (e.g.,twice) to inform the user that the button which is selected to beprogrammed is recognized. The user is supplied with a 20 digit codewhich contains both the frequency and code information. The digits ofthe 20 digit code are in the range of 1-4 (In contrast to the commonlyused digits in base four, i.e., 0-3). To make the task for the usereasier, the twenty digits are separated by dashes (e.g.,32124-11423-33123-21413-43411) as the user enters each group of fourdigits, the LED blinks once. However, after the entry of the last groupof digits the LED blinks multiple times (e.g., 5 times) to indicate thecompletion of code entry. At any point during the training procedure, ifthe training is unsuccessful due to delays in entering the digits a longLED blink is followed by a short blink alerts the user of unsuccessfultraining and the procedure is halted without any changes saved. FIG. 13depicts a flow chart for training procedure described above. In apreferred embodiment of the present invention, the codes do not reflecta one to one relationship of the location of the bits nor the frequencymap. I.e., the digits are scrambled in order to provide a methodologymore immune to be investigated/analyzed by hackers.

FIG. 14 depicts a block diagram for a transmitter which is capable ofproducing SparseCode. The SparseCode is programmed via key entryutilizing keys 302 into a controller circuit 300 which provides thefeedback to the user via LED 304. Controller circuit 300 could be amicro processor or a micro controller or FPGA or a custom controller.Upon pressing a key the baseband signal is generated by controllercircuit 300. SparseCode base band signal is generated by controller 300.The carrier frequency information is provided to an accurate radiofrequency generator such as DDS (Direct Digital Synthesis) or PLL(Phase-Locked Loop) frequency synthesizer 306. The advantage of DDS overa PLL is that it would provide sinusoidal signal with amplitude controlso the optimum levels with very low harmonic content is generated. Thebaseband output signal from controller 300 and the output of the signalsource 306 are fed to AM modulator 308 which in turn feeds band passfilter 310 feeding amplifier 312 and subsequently bandpass filter 314and antenna 316 is modulated by the data produced by the microcontroller. Band pass filtering is provided to reduce the harmonicsbefore and after the amplification.

Receiver

According to the present invention, the receiver is composed of aprocessor to handle a SparseCode. In a preferred embodiment of thepresent invention, a power saving arrangement is utilized. Sucharrangement provides a substantial advantage especially, when thesupplementary/universal receiver is battery operated.

The transmitter transmits a CW signal at a different frequency (f₂) thanthe operating frequency (f₁) which handles the data. The receiver istuned at the frequency (f₁) and is turned on for a small fraction oftime. When the auxiliary receiver which is a low power consumptionreceiver and operates at frequency (f₁) receives a signal at itsoperating frequency, it subsequently turns on the data receiveroperating at frequency (f₂).

FIG. 15 depicts a receiver with power saving receiver wherein Receiver-2represents any type of receiver, i.e., SparseCode, rolling code or fixedcode. In the absence of any receive signals, Receiver-2 is in sleepmode, i.e., Switch-2 is disconnected and the receiver does not take anypower from the power supply. Timer-1, is a clock circuit that provides ahigh signal only a small percentage of time, e.g., 2%. The output ofTimer-1 is connected to Switch-1. Each of the switches, i.e., Switch-1and Switch-2 can be implemented by a transistor switch such as a FET.Switch-1 provides the power supply connection to Receiver-1 when it isenabled. Switch-2 provides the power supply connection to Receiver-2when it is enabled. In order to save power, Timer-1 is turned on only asmall percentage of time enabling Receiver-1 for a small percentage oftime. During the time which Timer-1 turns on, Switch-1 is enabled and asa result Receiver-1 is temporarily turned on and antenna 320 receivesthe signal frequency (f₁) which in turn feeds Receiver-1 as a result ofreception of a signal at frequency (f₁), Receiver-1 produces a highsignal, turning on Timer-2, upon which Timer-2 stays on for a period oftime sufficient for reception and detection of signal by Receiver-2received via antenna 320 from the pertinent Transmitter. The transmittertransmits a CW signal at a different frequency (f₁) than the operatingfrequency (f₂) which handles the data. The receiver is tuned at thefrequency (f₁) and is turned on for a small fraction of time. Uponreception of signal at frequency (f₁) when timer 1 is on, Receiver-1provides a high signal to Timer-2 which enables Switch-2 temporarilysufficient for receiver-2 to receive and detect data and provide a highsignal output for activation of the pertinent opening/closing mechanism.

When the transmitter is a SparseCode of the type described in FIG. 14 orsimilar wherein a frequency synthesizer, the same transmitter canpotentially be used for generating both frequencies f₁ and f₂.

In another preferred embodiment of the present invention, the receiveris capable of receiving a master codes from a remote transmitter. Thisallows external programming for deactivating an old code or activating anew code. This requires a programmer module which is composed of atransmitter which transmits an activation master code followed by a codewhich needs to be activated and transmits a deactivation master codefollowed by a code which needs to be deactivated.

Supplementary Receiver

The described receiver according to the present invention can functionas a standalone receiver or in parallel with an existing receiver or aplurality of receivers. In such an arrangement, the receivers canfunction independent of each other since the receivers outputs arecontact closures and are connected which are in parallel. To avoidclimbing on a ladder for installation of the “supplementary receiver”the output ports of the receiver can be wired to the wall garage dooropening switch which is electrically the same point as the contactclosures. The supplementary receiver coding and frequency maps can beprovided to the universal garage door opener manufacturers for utilizingtheme in their universal transmitters. This by no means poses anysecurity compromises to the users as the only way to program a universaltransmitter is by entering the “training code” which is only known bythe user.

What is claimed is:
 1. A transmitter comprising: a signal generatorconfigured to generate a sparse code signal wherein said signal has asubstantially small duty cycle of about 0.5% and substantially smallpulse widths, with the distance between said pulses defined by saidsparse code, and sufficiently low carrier signal level so that thesignal can only be detected via a matched receiver.
 2. The transmitteraccording to claim 1 wherein different devices have different bandwidthsso that unmatched bandwidths producing sufficient inter-symbolinterference energy resulting in that the signal can only be detectedvia a matched receiver.
 3. The transmitter according to claim 1 whereindifferent devices have different carrier frequencies so that the signalcan only be detected via a matched receiver.
 4. A receiver that has thematching characteristic which can detect signals from a transmitterconstructed according to claim
 1. 5. A receiver that has the matchingcharacteristic which can detect signals from a transmitter constructedaccording to claim
 2. 6. A receiver that has the matching characteristicwhich can detect signals from a transmitter constructed according toclaim 3.